Although it appears to be a normal pearl, a pearl of wisdom will cause a cleric to increase 1 point in Wisdom if he or she retains the pearl for a 1 month period. 

The increase happens at the expiration of 30 days, but thereafter the pearl must be retained by the cleric and kept on his or her person, or the 1 point gain will be lost. 

Note that 1 in 20 of these magical pearls are cursed to work in reverse, but once the 1 point of Wisdom is lost, the pearl turns to powder, and the loss is permanent barring some magical restoration means such as a wish or Tome of Understanding.